Weatherability of xylitol-modified phenolic-bonded flakeboard

The purpose of this investigation was to determine if the water repellency exhibited by flakeboard bonded with a xylitol-modified phenolic adhesive would improve the performance of the flakeboard during 1 year of exterior exposure. Before and after exposure, static bending, internal bond, thickness swell and weight gain, and linear expansion of these flakeboards were compared to those properties of flakeboards bonded with a commercial phenolic adhesive. The static-bending properties of panels bonded with xylitol-modified phenolic adhesive or commercial phenolic adhesive were not significantly different before or after exterior exposure. Similarly, internal bond strength was not affected by exposure. However, in the 24-hour water-soak test, thickness swell and weight gain of panels bonded with xylitol-modified phenolic adhesive were less than that of panels bonded with the commercial phenolic adhesive, before and during exposure. After exposure, the thickness swell of panels was the same for both adhesive systems. Linear expansion from 30 to 90 percent relative humidity was the same for both adhesive systems before and after exposure. This indicates that initially the mechanism of action of the xylitol-modified phenolic adhesive is similar to that of wax. It reduces adsorption of liquid water, but not of water vapor.

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